The present invention generally relates to data storage, and more particularly, to a read/write head that couples radiation energy or other signals to and from a storage medium.
A typical optical storage system uses an optical head to focus a monochromatic optical beam to a small spot on a recording layer for reading and writing. The optical head may be positioned over the medium by a spacing greater than one wavelength, i.e., in a xe2x80x9cfar-fieldxe2x80x9d optical configuration where the optical energy is coupled between the optical head and the medium by light propagation. An optical head with a large numerical aperture can produce a small spot size which has a lower limit on the order of one half wavelength due to the diffraction limit. The areal density of an optical storage device, hence, is limited by this diffraction-limited spot size.
An optical storage system can also operate in a xe2x80x9cnear-fieldxe2x80x9d configuration where the optical head is spaced from the optical medium by a distance on the order of or less than one wavelength. The optical coupling between the optical head and the medium, therefore, can be effected by evanescent coupling, with or without light propagation. An effective numerical aperture of the optical head in such a near-field configuration can be greater than unity. Hence, a near-field optical storage system can achieve a focused beam spot size much less than one half wavelength and to realize a high areal storage density.
The optical head is a critical part of an optical storage system and its properties can significantly affect the overall performance of the system. In addition to the focusing of a read/write beam, the optical head also controls other operations of the system, including recording of data, signal detection, beam tracking on the data tracks, and grey code detection.
For example, many optical heads have an optical interfacing surface that couples optical radiation to and from the storage medium. This interfacing surface may be an optical surface of a lens, a small optical flat, or a transparent mesa formed as part of a lens. One technical challenge is to maintain this interfacing surface free of contaminants which may be formed on the interfacing surface from a variety of sources. One source is localized heating at and near the focused spot on the recording medium surface by absorption of a focused optical beam. Certain species on the recording medium surface may become desorbed due to the localized heating and transfer to adhere to the optical head. Other sources include material deposited on the optical head through intermittent contacts between the optical head and the medium surface, and particulates present in the disk drive.
Contaminants adhered to the interfacing surface in the path of the optical signals can adversely affect the signals by causing signal distortions. Such signal distortions, in turn, can lead to loss of tracking, track misregistration, data jitter, reduction in the signal-to-noise ratio, or other problems that degrade the performance or even cause malfunction of the system.
The present disclosure provides an optical data storage system having a cleaning mechanism that cleans an optical head by contacting an optical interfacing surface of the head to another element in a controlled manner, or placing the optical interfacing surface of the head in a close proximity of, or in at least partial contact with a surface of the storage medium.
The cleaning mechanism includes a detection module to detect and determine the degree of contamination of the interfacing surface of the optical head. The detection module measures a contamination-induced distortion in an optical signal received by the optical head from the optical storage medium. When such a distortion exceeds a tolerance range, the interfacing surface is cleaned in order to maintain the performance of the disk drive.
The cleaning mechanism may implement different ways of cleaning the interfacing surface of the optical head. In one embodiment, the cleaning mechanism is configured as a xe2x80x9con-demandxe2x80x9d mechanism which operates to clean the interfacing surface only when the system so requests. The cleaning mechanism may also be configured as an xe2x80x9cautomaticxe2x80x9d mechanism which automatically cleans the interfacing surface whenever a certain operation is performed, such as reading and writing data to the disk, loading or unloading the head. This two type of cleaning mechanisms may be combined in a disk drive.
In one implementation of the on-demand cleaning mechanism, the optical head may be controlled to briefly and lightly contact the interfacing surface with the surface of the storage medium so as to remove the contaminants from the interfacing surface.
In an optical disk drive where the optical head is suspended over the optical disk by an air bearing surface, the contact between the optical head and the disk surface for cleaning may be brought about by reducing the spinning speed of the disk so that the up-lifting force of the air bearing is reduced to allow a light contact. Another implementation reduces or turns off the power to the spindle motor that drives the disk for a brief period. The speed of the disk is so reduced that the desired light contact occurs and cleans the interfacing surface of the head.
When the interfacing surface of the optical head is an optical surface of a transparent mesa structure formed in the optical head, the above light contact can be caused by momentarily supplying sufficient heat to the mesa so that the thermal expansion of the mesa structure brings the interfacing surface into contact with the disk surface. In this implementation, the disk may be maintained at the speed for the normal operation during the brief contact. A heating coil or thin-film heater may be formed around the mesa structure to provide the heat without intercepting the optical path between the head and the disk.
In another implementation, the interfacing surface of the optical head is cleaned by briefly contacting a cleaning element during loading and unloading the optical head to and from the disk. The cleaning element is disposed relative to the ramp of the disk drive that receives the stinger engaged to the suspension arm of the optical head when the optical head is unloaded from or loaded onto the disk so that a cleaning surface of the cleaning element lightly touches the interfacing surface to remove contaminants every time the optical head is loaded or unloaded. During normal operation, if the detection module determines that the head needs cleaning, the disk drive can temporarily interrupt the operation and clean the optical head by performing an unload/load operation. Therefore, this mechanism can function both as an on-demand cleaning mechanism or as an automatic cleaning mechanism.
The automatic cleaning mechanism may also be implemented by placing the interfacing surface of the head in close proximity from a surface of the storage disk to prevent accumulation of contaminants. A spacing sensor, e.g., an acoustic emission sensor, or optical detection of mass transfer from the disk to the head, may be used to determine the position of the interfacing surface in the close proximity. The optical drive can operate continuously when the head is in close proximity of the disk during writing and reading and the interfacing surface is automatically cleaned.
Any of the above cleaning techniques may be used either individually or in a combination in a disk drive. Advantages of the invention include improvements in performance and reliability of a disk drive and reduction in maintenance over the lifetime of the disk drive.
These and other aspects and associated advantages of the present invention will become more apparent in light of the following detailed description, the accompanying drawings, and the appended claims.